In large endless non-metallic conveyor belts, which may have metal reinforcing cables therein, used to convey bulk material, there is a possibility of encountering a rip in the belt, for example, by a sharp object dropped thereon at the loading station. It is desirable promptly to detect such rips and, preferably, to shut down the conveyor belt upon such detection, thereby minimizing damage to the belt.
One such conveyor belt rip detector is disclosed in U.S. Pat. No. 3,792,459 issued to Snyder. In such rip detector plural antennas, which may be single electrical conductors, are embedded in the belt transversely to its length at spaced apart locations in the belt. An electrical signal is coupled by respective antennas from a transmitter to a receiver as the belt moves and the respective antennas pass in capacitive coupling relation with the transmitter and receiver at a rip detector station, and the receiver thus delivers an input signal to detector circuitry which interprets the same as an indication of satisfactory belt integrity. However, a broken antenna, for example at a place where the belt has been ripped will not couple the transmitter signal through to the receiver, and the detector then senses the same as an indication of the occurrence of a rip condition. The detector circuit in such patent is operative after the lapse of a predetermined time period corresponding to the passage of a given number of broken antennas past the rip detector station to produce a distinguishable output that activates an alarm and/or deactivates the conveyor belt drive.
A number of improvements for use in conveyor belt rip detectors are disclosed in U.S. Pat. No. 4,228,513 issued to Doljack. One of such improvements includes a means for detecting the progress of the conveyor belt to know when an antenna should be at the rip detector station. If there is no antenna present then, a prompt shutdown of the conveyor belt drive may be effected.
Further improvements are disclosed in U.S. application Ser. No. 288,882 filed July 31, 1981 in the names of Haylett et al. That disclosure relates to a digital phase shift circuit signal generator for improved rip detection capabilities. The circuit of that disclosure includes means accurately to adjust and to control the relative phase shift between the transmitted AC transmitter signal and the reference or demodulating signal so that the phase of the demodulating signal will be at least substantially the same as that of the AC transmitter signal. The entire disclosure of the aforementioned Haylett application, including the prior art patents and applications referred to therein, are hereby incorporated by reference into the instant application.
The present invention relates to improved electrical means for adjusting the synchronism between transmitted and received electrical signals and for determining, and particularly for providing an indication of, the phase shift relationship between such signals.
With the foregoing in mind, an object of the invention is to improve conveyor belt rip detector apparatus.
Another object of the instant invention is to detect the synchronous relationship between a transmitted signal and a reference signal to improve the rip detection capabilities of a conveyor belt system.
A further object is to tune a synchronous rip detector circuit of a conveying assembly.
These and other objects and advantages of the present invention will become more apparent from the following description.
To the accomplishment of the foregoing and related ends, the invention comprises the features hereinafter fully described in the specification and particularly pointed out in the claims, the following description and the annexed drawings setting forth in detail a certain illustrative embodiment of the invention, this being indicative, however, of but one of the various ways in which the principles of the invention may be employed.